The presence and properties of flavin monooxygenase (FMO) in liver of the marine teleost, turbot (Scophthalmus maximus) were examined in relation to organic xenobiotic metabolism and osmoregulation. 2. Hepatic microsomes of sexually mature fish contained NADPH-dependent FMO as evidenced by the conversion of N,N-dimethylaniline (DMA) to DMA-N-oxide, and immunorecognition of single bands (approximate apparent molecular weight of 55 kDa) by antibodies to mammalian FMO 1 and FMO 2. Additionally, Northern analysis using a full-length cDNA probe to mammalian FMO 1 revealed a single hybridizing band of approximately 2.5 kb. 3. No significant differences were seen between male and female turbot FMO with respect to DMA N-oxidase activity, levels of immunoreactive protein (with anti-FMO 1 or anti-FMO 2) and gene expression (hybridizing mRNA). 4. Hepatic microsomal DMA N-oxidase activity was inhibited by methimazole (an FMO substrate) and trimethylamine (TMA), but not by piperonyl butoxide (a P450 inhibitor). Inhibition by TMA is indicative of a role for FMO in osmoregulation, catalysing the conversion of TMA to TMA N-oxide. DMA N-oxidase activity was optimal at pH 8.8 and 25 degrees C, and displayed Michaelis-Menten kinetics with respect to DMA (apparent Km = 88 microM).
摘要
研究了海洋硬骨鱼大菱鲆（Scophthalmus maximus）肝脏中黄素单加氧酶（FMO）的存在情况及其性质，探讨了其与有机外源性物质代谢和渗透调节的关系。2. 性成熟鱼类的肝脏微粒体含有依赖NADPH的FMO，这可通过N，N - 二甲基苯胺（DMA）转化为DMA - N - 氧化物得以证明，并且用针对哺乳动物FMO 1和FMO 2的抗体对单一条带（表观分子量约为55 kDa）进行免疫识别也可证明。此外，使用针对哺乳动物FMO 1的全长cDNA探针进行的Northern分析显示出一条约2.5 kb的单一杂交带。3. 在DMA N - 氧化酶活性、免疫反应性蛋白水平（用抗FMO 1或抗FMO 2）和基因表达（杂交mRNA）方面，雄性和雌性大菱鲆的FMO没有显著差异。4. 肝微粒体DMA N - 氧化酶活性受到甲巯咪唑（一种FMO底物）和三甲胺（TMA）的抑制，但不受胡椒基丁醚（一种P450抑制剂）的抑制。TMA的抑制作用表明FMO在渗透调节中发挥作用，催化TMA转化为TMA N - 氧化物。DMA N - 氧化酶活性在pH 8.8和25℃时最佳，并且相对于DMA呈现米氏动力学（表观Km = 88 microM）。
